1. Field
The present invention relates to a counter, and more particularly, to a digital counter used in a CMOS (Complementary Metal Oxide Semiconductor) image sensor.
2. Description of the Related Art
The Complementary Metal Oxide Semiconductor (CMOS) image sensor (CIS) has been widely used as image input devices of mobile phone cameras or CCTVs. CMOS image sensors operating digitally include several thousand digital counters. These digital counters increase power consumption.
An n-bit digital counter includes n D-flip-flops, and is configured to receive external clock signals and increase the digital output value by 1 at each rising edge of the clock signal.
Power consumption in the digital counter occurs when a digital signal toggles/pulses, for example, when the digital signal transitions from a logic low level to a logic high level. In the conventional digital counter, the digital signal toggles at each cycle of the clock signal. Since power consumption occurs when a signal toggles, CMOS image sensor power consumption inevitably increases as the number of digital counters increases.